Wireless based positioning method and apparatus

ABSTRACT

A system and method is described herein to determine the physical location of a user within an edifice. At least three wireless access points, for example, 802.11 nodes, receives and transmits information to a handheld device in order to determine the location information.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application Ser.No. 61,050,641, filed May 6, 2008, which is incorporated herein byreference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a wireless based positioningmethod and apparatus that allows a user employing a handheld device todetermine his location in a building.

2. Background

The ability to employ wireless network access points, for example 802.11nodes, to determine a user's position information has been limited.These wireless networks, which are commonly available in most commercialenvironments, currently have limited use in terms of locationdeterminations because the network users need to access a map ordatabase containing advanced knowledge of the environment. Accordingly,there is a need for a system and method for wireless based positioningwithin a structure containing a wireless network.

SUMMARY OF THE INVENTION

Embodiments of the present invention satisfy the above need, whileproviding other advantages. Specifically, embodiments of the presentinvention allow a user to locate his position information with respectto wireless access nodes within a building, for example.

An embodiment of the present invention includes a method for determininga users position employing a wireless network, comprising:

-   -   providing an edifice containing the wireless network comprised        of a plurality of wireless access points throughout the edifice;    -   providing a handheld device operable to transmit and receive        transmissions from the plurality of wireless access points;    -   transmitting location information from the at least three        wireless access points to the handheld device;    -   receiving said transmitted location information at the handheld        device;    -   processing said transmitted location information to determine        location of said handheld device within the edifice.

Further method, system and apparatus embodiments are apparent from thedescription below.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is described with reference to the accompanyingdrawings. In the drawings, like reference numbers indicate identical orfunctionally similar elements.

FIG. 1 is an example of a floor plan of a building with wireless networkaccess points and a handheld device operable to locate a users positioninformation with respect to the wireless access points;

FIG. 2 is an example of a handheld device operable to obtain theposition information from the wireless access points;

FIG. 3 is an example of a flowchart describing the method of determininga users location information by using a wireless network.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 is an example of a floor plan 10 within a building with aplurality of wireless access points (WAP), for example 902.11 nodes,items 20-50 deployed throughout the building. A handheld device 15 canbe employed by a user to determine the device 15 positioning throughoutthe building where there is access to at least three wireless accesspoints.

Outdoors, position information is typically achieved by GPS technology,however, this technology does not function indoors. Several systemsexist which use extensive databases of wireless network signalcharacteristics to determine location, but these cannot be used wherethere is a lack of a database containing location information orpre-mapped location information. This is the case in buildings or otherlocations that have not been pre-mapped.

Wireless access nodes employ a protocol such as IEEE 802.11, or“Bluetooth” that allows users to receive and transmit information in anenclosed environment. The wireless access nodes are connected to by userdevices, which allows access to the internet or local data services. Inaddition to the information requested by the user of such devices, thenodes and the connected user devices send and receive informationrelated to the connection, such as the network name (usually called theSSID in the 802.11 protocol), available radio frequencies, availabledata transfer rates, and security restrictions. This connection relatedinformation is transmitted in specific fields of the protocol packets,which are standardized blocks of information organized in specific ways.Such fields could be used to notify user devices of the transmissionpower and the three dimensional location of the transmitting node,either by adapting existing fields of the protocol (such as the SSID) orusing extensions to the protocol.

The present invention employs parameters that each wireless access point(WAP) or 802.11 node can make available, via a field or fields of theprotocol, which are the transmitter power and the three dimensionallocation position of the WAP.

Transmitter power is encapsulated in a parameter, hereinafter referredto as k, which includes the power measured by a protocol compliantdevice (the Received Signal Strength (RSS) measurement in 802.11) at aknown distance from the WAP (e.g. 0.01-3 meters from the transmitter),and the square of said distance. This parameter is encoded in a protocolfield transmitted by the WAP

Determining k

The present invention requires a determination of the k parameter, whichis a measure of transmitter power at a fixed distance. This can beachieved by setting the receiver approximately 0.01-3 meters away fromeach WAP to be used for positioning and taking a set of RSSmeasurements. This is done for each available transmission power settingavailable on the WAPs, and the k parameter is determined at a specificdistance d_(o) established by convention, by the formula k=P(d_(o))d_(o)², where P(d_(o)) is the RSS value measured at said distance.

WAPs can be deployed on a floor of a building and most are alreadypre-existing in order to facilitate wireless access to the internet.Thus the present invention can easily be deployed in any commercialenvironment with WAPs. The WAPs, within their respective subscriber setidentifications (SSID), can be programmed to broadcast the value of kand their positions in a local x-y-z coordinate grid.

The three dimensional location position of the WAPs can take the form ofeither the Cartesian coordinates, typically referred to as X, Y and Z,or the latitude-longitude-elevation (LLE) coordinates used in geographiccoordinate systems. The present invention employs two types ofcoordinate systems. The first is using a local coordinate system, forinstance a grid based on the floor plan of a building, as the source ofthe WAP position. The second mode uses an external coordinate system,such as the World Geodetic System 1984 (WGS-84). The source of thesepositions may include a geographic survey, the Global Positioning System(GPS), or some other method of position measurement. These parameters(either XYZ or LLE) are encoded in a protocol field transmitted by theWAP.

Accordingly, FIG. 2 is an exemplary embodiment of the handheld device 15used to determine location position information, via atransmitter/receiver 60, operable to transmit and receive informationfrom the handheld device 15 and the WAPs. The processor 70 is employedto process the information received and transmitted, as detailed below,and memory 70 is used to store the processed information. In particular,the computer programs, when executed, enable the processor 70 toimplement the method of the present invention as illustrated in FIG. 3,for example, and detailed below. Where the invention is implementedusing software, the software may be stored in a computer program productand loaded into a computer system, such as the handheld 70, using memory65 and a communication interface 75.

FIG. 3 is exemplary of the method employed in the present invention.

Step 100 describes the step of measuring and determining the parameter kas described above, from each of the at least three WAPs.

Step 110 describes the handheld 15 receiving spatial coordinates fromeach of the at least three WAPs, via fields of the communicationprotocol

Step 120 describes receiving a radio signal power from each of the atleast three WAPs, to be used to determine the distance between thehandheld 15 and the at least three WAPs being used to determine locationposition information.

Step 130 describes estimating the distance based on the parameter k, andthe measured radio signal power of step 120.

Step 140 determining the users physical position based on the abovereceived information.

The present invention employs a form of lateration that will now bedescribed.

This method uses a novel form of lateration. Three or more spheres ofconstant ratio of distances, which are the locus of points where theratio of distances to two points with known three dimensional spatialcoordinates is constant, are calculated based on distance estimates tosaid points. In this method the distance estimates are calculated basedon measurements of the received radio signal power from radiotransmitters located at known spatial coordinates.

This method of lateration differs from the two previously known andwidely used techniques, commonly referred to as trilateration andmultilateration, as follows. Trilateration calculates the locus ofpoints of constant distance from a single point with known spatialcoordinates, and does so for at least three points. That istrilateration uses the distance estimates directly, without formingtheir ratio. Multilateration calculates the locus of points withconstant difference of distances, which is a hyperboloid, between twopoints with known spatial coordinates. Multilateration also requiresthree or more points and associated distance estimates.

This method of lateration, employed in the present invention, is alsodistinct from what is commonly referred to as triangulation, whichdetermines the angle between a known direction, for example geographicNorth, and the direction to points with known spatial coordinates.

The present invention employs a wireless network to determine userposition with WAPs and a handheld device facilitating the followingmethod.

A wireless network is setup to perform user position estimation usingthis method consisting of the following.

The method first determines the three dimensional spatial coordinates ofeach network WAP or transmitter. This can be accomplished using a map,geographic survey, the Global Positioning System (GPS), or buildingblueprints or floor plans. These coordinates can be relative to a localcoordinate system or relative to a global coordinate system such as theWGS-84. If using the method described herein or a system such as GPS,said coordinates could be determined coincidentally with onlineoperation (described below) and updated when changes occur.

The next step of the method includes determining the radio signal powerof each of the WAPs or transmitters at a fixed, predetermined distanceand determining the parameter k=P(d_(o))d_(o) ², where P(d_(o)) is thepower measured at said distance. This distance is the same for all ofthe said APs or transmitters. The k value is unique to each AP ortransmitter. In 802.11 protocol based devices a typical value of the kparameter is 0.01 milli-Watts for a reference distance of 1 meter. Theradio transmitter output power can be changed during online operations(described below), for example to conserve battery power on a mobilenetwork device, and thereby updating the k parameter in real-time. Inthis case, values of the k parameter for each possible radio transmitteroutput power are determined in this step.

The next step includes encoding the three dimensional spatialcoordinates and the k parameter of each of the WAPs or transmitters in afield or fields of the wireless communication protocol in use. Forexample in the 802.11 wireless LAN protocol the SSID field can be used.

The next step includes causing each of the WAPs or transmitters totransmit the protocol field or fields with encoded information encodedwithin continuously or at fixed time intervals.

The above procedure describes the initial set up for the actual methodof the present invention. In operation the method according to an aspectof the present invention includes the user measuring the radio signalpower of each of three or more WAPs or transmitters. The Usersimultaneously receives and decodes the protocol field or fieldscontaining the k parameter and three dimensional spatial coordinates ofeach of the WAPs or transmitters.

The user can then estimate his or her distance to each of said APs ortransmitters based on isotropic spherically symmetric energy propagation(one over r-squared law) based on the radio signal power measured andthe k parameter for each WAP or transmitter previously decoded.

The user can then calculate the parameters of the spheres of constantratio of distances for each unique pair of said APs and transmittersutilizing the distance estimates based on isotropic sphericallysymmetric energy propagation and the spatial coordinates of said WAPs ortransmitters. The parameters calculated consist of the three spatialcoordinates of the center of each of said spheres of constant ratio ofdistances and the radius of each of said spheres of constant ratio ofdistances.

The user determines the best estimate of his or her position byminimizing the difference between the distance from the estimate ofuser's position and the center of the spheres of constant ratio ofdistances determined above and the radius of each of said spheres ofconstant ratio of distances.

As a first step, the general equations for fixing the position of areceiver using the ratio of distance measurements is shown. Thesedistances are based on RSS from a set of transmitters at known referencepoints. The following are assumptions about the signal propagation.

The equation for distance:d _(i) ²=(x _(i) =x ₀)²+(y _(i) −y ₀)²+(z _(i) −z ₀)²  (1)where (x₀, y₀, z₀) is the unknown position of the receiver, (x_(i),y_(i), z_(i)) is the known position of the i-th transmitter, and d_(i)is the unknown but measurable distance between them. Generically we canexpect the signal strength, or power, to be expressible as a function ofdistance. That isP _(i)=ƒ(d _(i);ρ_(i)).for the i-th measurement where ρ_(i) is the set of parameters describingthe transmitter. The function ƒ(d; ρ) describes the propagation of thesignal. Now we can express distance as a function of power asd _(i)=ƒ⁻¹(P _(i);ρ_(i))where ƒ⁻¹ is the function inverse.

The ratio of two distance measurements is as follows:

$\frac{\mathbb{d}_{i}}{\mathbb{d}_{j}} = {\frac{f^{- 1}( {P_{i};\rho_{i}} )}{f^{- 1}( {P_{j};\rho_{j}} )}.}$

Multiplying both sides by dj and squaring we have

$d_{i}^{2} = {{d_{j}^{2}( \frac{f^{- 1}( {P_{i};\rho_{i}} )}{f^{- 1}( {P_{j};\rho_{j}} )} )}^{2}.}$

Now utilizing Equation (1)

${( {x_{i} - x_{0}} )^{2} + ( {y_{i} - y_{0}} )^{2} + ( {z_{i} - z_{0}} )^{2}} = {\begin{pmatrix}\begin{matrix}{( {x_{j} - x_{0}} )^{2} +} \\{( {y_{j} - y_{0}} )^{2} +}\end{matrix} \\( {z_{j} - z_{0}} )^{2}\end{pmatrix}( \frac{f^{- 1}( {P_{i};\rho_{i}} )}{f^{- 1}( {P_{j};\rho_{j}} )} )^{2}}$

After gathering terms and completing the square once each for x₀, y₀,and z₀, we have

$\begin{matrix}{{{( {x_{0} - x_{cij}} )^{2} + ( {y_{0} - y_{cij}} )^{2} + ( {z_{0} - z_{cij}} )^{2}} = d_{cij}^{2}}{where}} & (2) \\{{x_{cij} = \frac{x_{i} - {Q_{ij}x_{j}}}{1 - Q_{ij}}}{y_{cij} = \frac{y_{i} - {Q_{ij}y_{j}}}{1 - Q_{ij}}}{z_{cij} = \frac{z_{i} - {Q_{ij}z_{j}}}{1 - Q_{ij}}}{d_{cij}^{2} = \frac{Q_{ij}d_{ij}^{2}}{( {1 - Q_{ij}} )^{2}}}} & (3)\end{matrix}$

The squared ratio of the distances, or inverted propagation functionsare as follows:

$\begin{matrix}\begin{matrix}{Q_{ij} = ( \frac{d_{i}}{d_{j}} )^{2}} \\{= ( \frac{f^{- 1}( {P_{i};\rho_{i}} )}{f^{- 1}( {P_{j};\rho_{j}} )} )^{2}}\end{matrix} & (4)\end{matrix}$

Equation (2) is the equation of a sphere. The unknowns are the positionof the receiver, (x₀, y₀, z₀), which describe a point on the surface ofthe sphere.

By noting thatQ _(ji) ⁻¹ =Q _(ij)it can be seen that equations (3) and equation (4) are invariant underthe swap i→j and j→i; so more generally, with N measurements theposition of the transmitter is at the intersection of the

$N = \frac{n( {n - 1} )}{2}$unique spheres. Location estimation using these spheres of constantratio of distances then constitutes finding their intersection, or thebest fit.

The Cartesian coordinate system can be translated or rotated such thatany point lies on the origin, and any other point lies on the x-axis. Ifa transformation is completed such that the point x_(j) is at the originand the point x_(i) is on the x-axis, the sphere has its center at

$x_{cij} = \frac{x_{i}}{1 - Q_{ij}}$which demonstrates that the center of the sphere of constant ratio ofdistances lies on the line connecting the two reference points.Furthermore it can be noted thatd _(cij)=√{square root over (Q _(ij))}|x _(cij)|.and that the distance between the point xi and the sphere center is|x _(i) −x _(cij) |=Q _(ij) |x _(cij)|.

Now if Q_(ij)>1 then x_(cij) has the opposite sign of x_(i), and|xc_(ij)|<d_(cij)<|x_(i)−x_(cij)|, so the sphere intersects the lineconnecting reference points x_(i) and x_(j) between the two points.Similarly if Q_(ij)<1 then |xc_(ij)|>|x_(i)| and is on the same side ofthe origin as x_(i). It then follows that|x_(i)−x_(cij)|<d_(cij)<x_(cij) so the sphere again intersects theconnecting line between the two reference points.

Based on these two cases, the center of the sphere of constant ratio ofdistances is never between the two reference points (or transmitters).The case Q_(ij)=1 was left out of the previous discussion, but thatcorresponds to a straight line perpendicular to the connecting linebetween the reference points, intersecting at the midpoint. This clearlydoes not invalidate the conclusions.

Equation (2) can be used to determine the most likely location, (x*, y*,z*), in the presence of measurement errors. The error between a locationand the set of possible locations defined by a pair of signal strengthmeasurements can be expressed as a difference in distances:Δd _(ij)=√{square root over ((x _(c) _(ij) −x)²+(y _(c) _(ij) −y)²+(z_(c) _(ij) −z)²)}{square root over ((x _(c) _(ij) −x)²+(y _(c) _(ij)−y)²+(z _(c) _(ij) −z)²)}{square root over ((x _(c) _(ij) −x)²+(y _(c)_(ij) −y)²+(z _(c) _(ij) −z)²)}−√{square root over (d _(c) _(ij)²)}.  (5)

The sum of squared errors for all measurements is then minimized:

$\begin{matrix}{( {x^{*},y^{*},z^{*}} ) = {\underset{({x,y,z})}{\arg{\;\;}\min}{\sum\limits_{{i = 1},{j = {i + 1}}}^{{i = {N - 1}},{j = N}}( {\Delta\; d_{ij}} )^{2}}}} & (6)\end{matrix}$using any of the standard techniques for nonlinear least squaresminimization.

A model for the propagation of radio signals, such as those radiosignals employed by the present invention, and for example those radiosignals employed by the 802.11 wireless networking protocol, will bedescribed next. The model to be developed here is based on the wellknown log-distance and partition loss models.

In free space an isotropic radiator follows the Friis free spaceequation

$\begin{matrix}{{P_{r}(d)} = \frac{P_{t}G_{t}G_{r}\lambda^{2}}{( {4\pi} )^{2}{Ld}^{2}}} & (7)\end{matrix}$where P_(r) is received power, P_(t) is transmitted power, G_(t) andG_(r) are the transmitter and receiver gains, λ is the wavelength, and Lis a non-propagation loss factor. Next define a single parameter k forthe transmitter by measuring P_(r) at a reference distance

$\begin{matrix}{\begin{matrix}{{P_{r}( {d;k} )} = \frac{{P_{r}( d_{0} )}d_{0}^{2}}{d^{2}}} \\{= {\frac{k}{d^{2}}.}}\end{matrix}{Now}{d^{2} = \frac{k}{P_{r}}}{And}{Q_{ij} = {( \frac{k_{i}}{k_{j}} ){( \frac{P_{rj}}{P_{ri}} ).}}}} & (8)\end{matrix}$

This estimate of Q_(ij) does not depend on the characteristics of thereceiver, but only on the ratio of k_(i) to k_(j). This then imposes theonly calibration requirement of this method—the transmitter parameter kmust be reported such that it is in the correct ratio to that of othertransmitters.

Indoor propagation is illustrated by the following:

$\begin{matrix}{{{\hat{P}}_{r}\lbrack {{dB}\; m} \rbrack} = {{{P_{r}( d_{0} )}\lbrack {{dB}\; m} \rbrack} - {10n\;{\log( \frac{d}{d_{0}} )}} - {\sum\limits_{w}^{W}{PAF}_{w}}}} & (9)\end{matrix}$where {circumflex over (P)}_(r) is measured received power (the RSS inthe 802.11 protocol), n is the propagation exponent (which replaces 2 inthe Friis model), and PAF_(w) is the attenuation factor for partition w,which could be any general obstruction including walls and floors. Thehat notation ^ will be used to denote measured quantities (as opposed totheoretical or calculated) and the [dBm] indicates that this is alogarithmic expression with units of decibels relative to 1 mW.

Upon switching to units of mW this becomes

$\begin{matrix}{{{\hat{P}}_{r}\lbrack {m\; W} \rbrack} = \frac{k}{d^{n}10^{\beta}}} \\{= {\frac{P_{r}( {{d;k},n} )}{10^{\beta}}.}}\end{matrix}$ where$\beta = {\frac{\underset{w}{\sum\limits^{W}}{PAF}_{w}}{10}.}$

Now the measured distance ratio is

$\begin{matrix}{{\hat{Q}}_{ij} = ( \frac{k_{i}{\hat{P}}_{rj}}{k_{j}{\hat{P}}_{ri}} )^{\frac{2}{n}}} & (10)\end{matrix}$and so

${\hat{Q}}_{ij} = ( \frac{k_{i}10^{\beta_{j}}P_{rj}}{k_{j}10^{\beta_{i}}P_{ri}} )^{\frac{2}{n}}$

Now define this in terms of the propagation error

$\begin{matrix}{{{\hat{Q}}_{ij} = {ɛ_{ij}Q_{ij}}}{where}{ɛ_{ij} = {10^{\frac{2}{n}{({\beta_{j} - \beta_{i}})}}.}}} & (11)\end{matrix}$

This error depends only on the difference in the propagation paths. Thisis the principle result of this analysis. It shows that even undersignificant attenuation in the propagation paths due to variousobstructions, the estimated ratio of the distances to the transmitterscan still be relatively accurate if the two propagation paths aresimilar.

A comparison of equations (7), (8). and (10) yields that this resultminimizes any calibration effort required. The receiver gain is constantfor both power measurements, and as long as the ratio of the kparameters is correct no absolute accuracy in the power (or RSS)measurements is required.

This method of the present invention opens the possibility of extendingthe 802.11 protocol to support positioning services by allowing eachtransmitting device to provide its power (k) and its position. This canbe done using existing fields, but ideally new fields will be added. Avery close analogy is the transmission of satellite ephemeris data inthe GPS system. Such an extension to the 802.11 protocol would allow anymobile client to calculate its own position using only the receivedsignals at that position, with no other knowledge of its environment.

Such an extension can implemented using the SSID. As described in [10],this is 32 ASCII octets. The parameter k, and the position (x₀, y₀, z₀)of each transmitter can be encoded within the SSID string for eachaccess point, which then broadcasts this string as part of its otherwisenormal operation. In typical consumer devices the SSID can be set usingan html configuration utility over an http connection to the device,which in practice limits the SSID to the printable characters.

An additional aspect of the present invention employs a method allowingfor bit compression. Typically in order to display or transmit binarystructures in printable character form, Base16 (Hexadecimal) notation isused. According to an aspect of the present invention, each four bitbinary block within the binary structure is represented by one of thestandard 16 hexadecimal characters (0-9, A-F).

A standard ASCII character is represented in 32 bits, but hexadecimalnotation yields only 4 bits of resolution. In other words, the 16possibilities (0-9, A-F) only represent four bits of data, yet require32 bits to store.

The primary purpose of the B64 algorithms is to take advantage of someof the wasted space in a standard ASCII character Hexadecimalrepresentation, to save 50% more binary data in the same amount of ASCIIcharacter space.

This is accomplished by using a Base64 (B64) notation, comprised of 64standard printable characters (in order: 0-9, A-Z, a-z, $, &). Thisallows 6 bits of resolution per ASCII character, a gain (or compressionrate) of 50%.

Although this aspect of the present invention provides for an address 32bit native structure, the structures can be any length.

The method employs three basic parts, an ENCODE portion, a DECODEportion, and a CONVERT portion.

The ENCODE portion employs the following method: passing the list ofnumbers to be encoded one at a time to process A2 (below) until done,A2—Convert N to a string representation of the 32 bits, preserving thenative structure, and append it to a resulting string, A3—Pass 6 bits ata time from the resulting string to process A4 (below) until done. Zerofill the end of the last pass if less than 6 bits remain, A4—Convert the6 bits into a B64 character representation, and append to create astring of B64 characters, A5—Return the list of numbers in a B64notation string of printable ASCII characters.

The DECODE portion continues this aspect of the present invention bypassing the B64 notation characters one at a time to process B2 (below)until done. B2—Convert the B64 character to 6 bit binary stringrepresentation, and append it to a resulting string. B3—Pass 32 bits ata time to process B4 (below) until done. B4—Convert the 32 bits back tothe native number structure and add to output array of numbers, this isfurther described in the CONVERT method below. B5—Return the array ofnumber structures converted from B64 notation. The CONVERT portionincludes passing 4 bits at at a time and converting the 4 bits tostandard hexadecimal representation and appending the resultingcharacter string, then converting the hexadecimal characterrepresentation back to the original structure, and finally returningdecoded N to the original binary format.

The present invention has been described above with the aid offunctional building blocks and method steps illustrating the performanceof specified functions and relationships thereof. The boundaries ofthese functional building blocks and method steps have been arbitrarilydefined herein for the convenience of the description. Alternateboundaries can be defined so long as the specified functions andrelationships thereof are appropriately performed. Also, the order ofmethod steps may be rearranged. Any such alternate boundaries are thuswithin the scope and spirit of the claimed invention. One skilled in theart will recognize that these functional building blocks can beimplemented by discrete components, application specific integratedcircuits, processors executing appropriate software and the like or anycombination thereof. Thus, the breadth and scope of the presentinvention should not be limited by any of the above-described exemplaryembodiments, but should be defined only in accordance with the followingclaims and their equivalents.

1. A method for determining a users position employing a wirelessnetwork, said method comprising: providing an edifice containing thewireless network comprised of a plurality of wireless access pointsthroughout the edifice; providing a handheld device operable to transmitand receive transmissions from the plurality of wireless access points;transmitting location information from the at least three wirelessaccess points to the handheld device; receiving said transmittedlocation information at the handheld device; processing said transmittedlocation information to determine location of handheld device within theedifice; wherein said transmitted location information includesdetermining the three dimensional spatial coordinates of each networkaccess point by using a floor plan of the edifice, determining the radiosignal power of each network access point at a fixed predetermineddistance, encoding said spatial coordinate information and radio signalpower, transmitting said encoded spatial coordinate information andradio signal power at a fixed predetermined distance, receiving saidencoded information, and decoding and comparing said information foreach access point with measured radio signal power of that access pointat the location of the handheld device, wherein GPS information is usedto determine the three dimensional spatial coordinate of one or more ofthe access points, and wherein said encoding and comparing furthercomprising: providing the measured radio signal power of two of the atleast three access points and the predetermined radio power of each at afixed predetermined distance to calculate a squared ratio of theestimated distances to two of the at least three access points beingcompared by the following, where${Q_{ij} = {( \frac{k_{i}}{k_{j}} )( \frac{P_{rj}}{P_{ri}} )}};$providing the squared ratio of the estimated distances to the two of theat least three access points being compared and the three dimensionalspatial coordinates of the two of the at least three access points beingcompared to calculate the three dimensional coordinates of the centerand the radius of a sphere forming the locus of all points where theratio of the estimated distances is constant:$x_{cij} = \frac{x_{i} - {Q_{ij}x_{j}}}{1 - Q_{ij}}$$y_{cij} = \frac{y_{i} - {Q_{ij}y_{j}}}{1 - Q_{ij}}$$z_{cij} = \frac{z_{i} - {Q_{ij}z_{j}}}{1 - Q_{ij}}$${d_{cij}^{2} = \frac{Q_{ij}d_{ij}^{2}}{( {1 - Q_{ij}} )^{2}}};$providing these parameters to calculate the distance between a threedimensional spatial coordinate and the surface of the sphere defined bythese parameters:Δd _(ij)=√{square root over ((x _(c) _(ij) −x)²+(y _(c) _(ij) −y)²+(z_(c) _(ij) −z)²)}{square root over ((x _(c) _(ij) −x)²+(y _(c) _(ij)−y)²+(z _(c) _(ij) −z)²)}{square root over ((x _(c) _(ij) −x)²+(y _(c)_(ij) −y)²+(z _(c) _(ij) −z)²)}−√{square root over (d _(c) _(ij) )};determining the three dimensional spatial coordinates by minimizing thedistance between a three dimensional spatial coordinate and the surfaceof the sphere and using the three dimensional coordinates as theestimate of the three dimensional spatial coordinates of the handhelddevice.
 2. The method as claimed in claim 1, wherein said processingfurther comprises: measuring radio signal power of the at least threewireless access points; receiving spatial coordinates of the at leastthree wireless access points; estimating the distance from the handhelddevice to the at least three wireless access points by processing themeasured radio signal power and the received spatial coordinates;determining the location of the handheld device within the edifice bycomparing the estimated distance to the predetermined locations of theat least three access points within the edifice.
 3. A system fordetermining a users position employing a wireless network, said methodcomprising: an edifice containing the wireless network comprised of aplurality of wireless access points throughout the edifice operable totransmit and receive location information from the at least threewireless access points; a handheld device operable to transmit andreceive transmissions from the plurality of wireless access points andprocess said transmissions from the wireless access points to determinelocation information of the users within said edifice; wherein saidtransmitted location information includes determining the threedimensional spatial coordinates of each network access point by using afloor plan of the edifice, determining the radio signal power of eachnetwork access point at a fixed predetermined distance, encoding saidspatial coordinate information and radio signal power, transmitting saidencoded spatial coordinate information and radio signal power at a fixedpredetermined distance, receiving said encoded information, and decodingand comparing said information for each access point with measured radiosignal power of that access point at the location of the handhelddevice, wherein GPS information is used to determine the threedimensional spatial coordinate of one or more of the access points, andwherein said encoding and comparing further comprising: providing themeasured radio signal power of two of the at least three access pointsand the predetermined radio power of each at a fixed predetermineddistance to calculate a squared ratio of the estimated distances to twoof the at least three access points being compared by the following,where${Q_{i,j} = {( \frac{k_{i}}{k_{j}} )( \frac{P_{r_{j}}}{P_{r_{i}}} )}};$providing the squared ratio of the estimated distances to the two of theat least three access points being compared and the three dimensionalspatial coordinates of the two of the at least three access points beingcompared to calculate the three dimensional coordinates of the centerand the radius of a sphere forming the locus of all points where theratio of the estimated distances is constant: $\begin{matrix}{x_{c_{ij}} = \frac{x_{i} - {Q_{ij}x_{j}}}{1 - Q_{ij}}} \\{y_{c_{ij}} = \frac{y_{i} - {Q_{ij}y_{j}}}{1 - Q_{ij}}} \\{z_{c_{ij}} = \frac{z_{i} - {Q_{ij}z_{j}}}{1 - Q_{ij}}} \\{d_{c_{ij}}^{2} = \frac{Q_{ij}d_{jj}^{2}}{( {1 - Q_{ij}} )^{2}}}\end{matrix};$ providing these parameters to calculate the distancebetween a three dimensional spatial coordinate and the surface of thesphere defined by these parameters:Δd _(ij)=√{square root over ((x _(c) _(ij) −x)²+(y _(c) _(ij) −y)²+(z_(c) _(ij) −z)²)}{square root over ((x _(c) _(ij) −x)²+(y _(c) _(ij)−y)²+(z _(c) _(ij) −z)²)}{square root over ((x _(c) _(ij) −x)²+(y _(c)_(ij) −y)²+(z _(c) _(ij) −z)²)}−√{square root over (d _(c) _(ij) )};determining the three dimensional spatial coordinates by minimizing thedistance between a three dimensional spatial coordinate and the surfaceof the sphere and using the three dimensional coordinates as theestimate of the three dimensional spatial coordinates of the handhelddevice.